The proposed study's overarching goal is to reduce the ethnic disparities in illicit drug use, cigarette use, and HIV between Hispanic and non-Hispanic youth. This goal will be accomplished by four aims: AIM 1 is to evaluate the effectiveness of Familias Unidas, relative to Community Practice (i.e., standard prevention services), in preventing illicit drug use; AIM 2 is to evaluate the effectiveness of Familias Unidas, relative to Community Control, in preventing cigarette use; AIM 3 is to evaluate the effectiveness of Familias Unidas, relative to Community Control, in preventing unprotected sexual behavior; and AIM 4 is to assess the extent to which family functioning mediates the effects of the intervention on illicit drug use, cigarette use, and unprotected sexual behavior. Twenty four middle schools with a total sample of 744 Hispanic adolescents from a wide geographic area of Miami-Dade County will be randomized using a block design to one of two conditions: Familias Unidas or Community Practice. The Familias Unidas intervention has been evaluated and found to be efficacious in two separate randomized controlled trials. In the first study (Pantin et al., 2003), Familias Unidas was shown to be efficacious relative to a no intervention control condition in increasing family functioning and reducing behavior problems (Prado et al., 2006), risk factors for youth illicit drug use and unprotected sex. In the second randomized controlled trial (Prado et al., in press), Familias Unidas was found to be efficacious, relative to two attention control conditions, in preventing cigarette use and illicit drug use. Familias Unidas was also found to be efficacious relative to both of the control conditions in preventing/reducing unprotected sexual behavior at last sexual intercourse. Finally, family functioning was found to mediate the effects of intervention condition on the outcomes. Hierarchical Linear Modeling (HLM) will be used to test: (H1) Familias Unidas will be more effective than Community Practice in reducing illicit drug use over time; (H2) Familias Unidas will be more effective than Community Practice in reducing cigarette use over time; and (H3) Familias Unidas will be more effective than Community Practice in reducing unprotected sexual behavior over time. Additionally HLM will be used to determine whether (H1a) the effect of Familias Unidas on illicit drug use will be partially mediated by family functioning; (H2a) the effect of Familias Unidas on cigarette use will be partially mediated by family functioning and (H3a) the effect of Familias Unidas on unprotected sexual behavior will be partially mediated by family functioning.